Every once in a while there is trouble in a Revit project and you may want to know just who has been in the project. I mean e-v-e-r-y body.
To find out, open the folder "*_backup" that Revit makes with the same name as the project follwed by _backup. In there find a file named "users.dat".
You can open it with notepad. It's not nicely formatted, but it is a list of the login names of every user that has ever accessed the project.
Do yourself a favor and don't edit the file in anyway. Just copy the text out of this file and paste it somewhere to clean it up.